Table Of ContentHybrid Polymer Solar Cells
Hybrid Polymer Solar Cells
PROEFSCHRIFT
ter verkrijging van de graad van doctor aan de Technische Universiteit
Eindhoven, op gezag van de Rector Magnificus, prof.dr. R.A. van Santen,
voor een commissie aangewezen door het College voor Promoties in het
openbaar te verdedigen op maandag 24 januari 2005 om 16.00 uur
door
Waldo Joseph Elisabeth Beek
geboren te Roermond
Dit proefschrift is goedgekeurd door de promotoren:
prof.dr.ir R.A.J. Janssen
en
prof.dr. M.D. McGehee
This research has been financially supported by the Council for the Chemical Sciences of the
Netherlands Organization for Scientific Research (CW-NWO).
Omslagontwerp: Jan-Willem Luiten
Druk: universiteitsdrukkerij, TU/e
CIP-DATA LIBRARY TECHNISCHE UNIVERSITEIT EINDHOVEN
Beek, Waldo J.E.
Hybrid polymer solar cells / door Waldo J.E. Beek. – Eindhoven :
Technische Universiteit Eindhoven, 2005.
Proefschrift. - ISBN 90-386-2796-3
NUR 913
Subject headings: solar cells / conducting polymers / photoinduced electron transfer / polymer
morphology; composites / hybrid organic-inorganic materials / nanoparticles; metal oxides / zinc
oxide
Trefwoorden: zonnecellen / geleidende polymeren / fotogeïnduceerde elektronenoverdracht /
composietpolymeren; morfologie / organische – anorganische hybride materialen / nanodeeltjes;
metaaloxiden / zinkoxide
Table of Contents
Table of Contents
Chapter 1 Introduction
1.1 Hybrid materials...........................................................................................................................2
1.2 Solar cells.....................................................................................................................................3
1.2.1 Solar cell efficiencies...............................................................................................................4
1.2.2 Silicon solar cells.....................................................................................................................4
1.2.3 Polymer solar cells...................................................................................................................6
1.2.4 Dye-sensitized solar cells.........................................................................................................8
1.2.5 Hybrid polymer solar cells.....................................................................................................10
1.3 Objective and outline of this thesis.............................................................................................14
References and notes................................................................................................................................16
Chapter 2 Heterosupramolecular chemistry:
Heterosupermolecules from organic π-conjugated systems and TiO nanoparticles as model compounds for
2
electron transfer studies
2.1 Introduction to heterosupramolecular chemistry........................................................................22
2.2 TiO nanoparticle synthesis and characterization.......................................................................23
2
2.2.1 TiO nanoparticle preparation................................................................................................23
2
2.2.2 Compositional analysis..........................................................................................................23
2.2.3 Size analysis...........................................................................................................................25
2.3 Electron transfer in heterosupramolecular assemblies................................................................26
2.3.1 Formation of heterosupramolecular assemblies.....................................................................26
2.3.2 Static photoluminescence quenching by photoinduced electron transfer...............................28
2.3.3 Structure of the oligomer used in a heterosupermolecule......................................................30
2.4 Spacer length dependence of photoinduced electron
transfer in heterosupermolecules................................................................................................30
2.4.1 Distance dependence of charge transfer rate constants in the nonadiabatic
weak-coupling regime............................................................................................................30
2.4.2 Heterosupramolecular assemblies with carboxylic acid linkers.............................................31
2.4.3 Heterosupramolecular assemblies with phosphonic acid linkers...........................................32
2.5 Conclusions................................................................................................................................36
2.6 Experimental..............................................................................................................................36
References and notes................................................................................................................................41
Table of Contents
Chapter 3 ZnO nanoparticles for application in bulk heterojunction solar cells
3.1 Introduction................................................................................................................................44
3.2 Synthesis of soluble non-surfactant coated ZnO nanoparticles..................................................47
3.3 Characterization of ZnO nanoparticles and rods........................................................................48
3.3.1 Size and composition analysis of ZnO nanoparticles.............................................................48
3.3.2 Photo-physical characterization of ZnO nanoparticles...........................................................51
3.3.3 Cyclic voltammetry and current-voltage measurements........................................................53
3.4 Conclusions................................................................................................................................55
3.5 Experimental..............................................................................................................................55
References and notes................................................................................................................................58
Chapter 4 Photovoltaic devices from zinc oxide nanoparticles and conjugated polymers
4.1 Introduction................................................................................................................................62
4.2 Characterization of the solar cell performance...........................................................................64
4.3 Observation of a photovoltaic effect in bulk heterojunction solar cells
from ZnO nanoparticles and MDMO-PPV.................................................................................66
4.4 Initial screening of relevant parameters......................................................................................66
4.5 Effect of the layer thickness and vol.-% ZnO on the photovoltaic performance........................68
4.6 Incident light power dependency measurements........................................................................70
4.7 Calculation of the AM1.5 performance of the optimized solar cell............................................72
4.8 Investigation of surfactant effects and application of ZnO nanorods.........................................75
4.9 Degradation of the nc-ZnO:MDMO-PPV solar cell performance
by UV illumination.....................................................................................................................77
4.10 Application of regio-regular poly(3-hexylthiophene) in hybrid solar cells................................78
4.11 Charge carrier transport in nc-ZnO:MDMO-PPV blends...........................................................80
4.12 Conclusions................................................................................................................................82
4.13 Experimental..............................................................................................................................82
References and notes................................................................................................................................85
Table of Contents
Chapter 5 Characterization of nc-ZnO:conjugated polymer bulk heterojunctions
5.1 Introduction................................................................................................................................88
5.2 Photo-physical characterization of nc-ZnO:conjugated polymer composites............................89
5.2.1 UV-vis absorption spectroscopy............................................................................................89
5.2.2 Photoluminescence spectroscopy...........................................................................................90
5.2.3 Photoinduced absorption spectroscopy..................................................................................93
5.2.4 Flash photolysis time-resolved microwave conductivity.......................................................95
5.3 Morphology studies on nc-ZnO:MDMO-PPV composites........................................................97
5.3.1 Transmission electron microscopy.........................................................................................98
5.3.2 Tapping-mode atomic force microscopy................................................................................99
5.4 Conclusions..............................................................................................................................104
5.5 Experimental............................................................................................................................106
References and notes..............................................................................................................................108
Chapter 6 Hybrid ZnO:polymer bulk heterojunction solar cells from a ZnO precursor
6.1 Introduction..............................................................................................................................112
6.2 Sol-gel chemistry using ZnO precursors..................................................................................112
6.3 Conversion of the precursor into crystalline ZnO....................................................................113
6.4 ZnO precursor:MDMO-PPV blends.........................................................................................114
6.4.1 Effect of annealing on the film thickness of prec-ZnO:MDMO-PPV blends......................115
6.4.2 Effect of precursor condensation on the optical properties of
prec-ZnO:MDMO-PPV blends............................................................................................116
6.5 Photovoltaic effect in devices made from ZnO precursors and MDMO-PPV..........................119
6.5.1 Characterization of the photovoltaic effect..........................................................................119
6.5.2 Effect of the processing parameters on the photovoltaic performance.................................120
6.6 Characterization of the morphology of prec-ZnO:MDMO-PPV blends..................................121
6.7 Conclusions..............................................................................................................................124
6.8 Experimental............................................................................................................................125
References and notes..............................................................................................................................127
Samenvatting
Summary
Curriculum Vitae
List of Publications
Dankwoord
Chapter 1
Introduction
Abstract
This chapter introduces the concept and application of hybrid materials. Different strategies towards
hybrid materials are reviewed and discussed with respect to application in solar energy conversion
devices. Using present knowledge from polymer bulk heterojunction and dye-sensitized solar cells, the
design of a simple, and in essence low cost, hybrid solar cell based on metal oxides and conjugated
polymers is presented.
Chapter 1
1.1 Hybrid materials
The words ´hybrid materials´ stand for a combination of (a minimum of) two materials of a
different nature into a new one having the combined properties of the starting materials together with
some added value. The hybrid materials’ properties are often superior to the sum of the intrinsic
properties of the components and often have a functionality that is not present in either of the
individual materials1. In a historical perspective, the utilization of hybrid materials goes far back. A
nice example is ‘adobe’, being a mixture of clay and straw, used in bricks and walls for buildings in
rural areas. Its modern equivalent would be steel reinforced concrete, one of the building blocks of
our modern society.
In recent years an increasing amount of
scientific publications concerning hybrid
organic – inorganic materials can be 800
700
noticed (figure 1.1). The search for these s
n
o 600
materials is driven by the desire for ati
c 500
bli
u
combining the properties of inorganic p 400
of
materials and organic (polymeric) er 300
b
m 200
u
materials, to create new, enhanced, and n
100
appealing performance. Early applications 0
1 1 1 1 1 1 1 1 1 1 2 2 2 2
of hybrid organic-inorganic systems can 99 99 99 99 99 99 99 99 99 99 00 00 00 00
0 1 2 3 4 5 6 7 8 9 0 1 2 3
be found in paints, UV shields2, and
scratch resistant automotive coatings3. Figure 1.1 Histogram taken from the Chemical Abstracts
Hybrid material science has been used to displaying the number of publications using the term:
improve optical4,5, thermal, and ´Hybrid Organic Inorganic Materials’.
mechanical6 properties of polymers. More
recently the attention is drawn towards the electrical7 properties of hybrid organic-inorganic materials.
The discovery of conducting polymers by Alan MacDiarmid, Hideki Shirakawa, and Alan Heeger
in 1977, and the ability to dope these polymers to cover the full range from insulator to metal8, has
created a new field of research at the crossroads of chemistry and condensed matter physics. These
newly discovered conjugated polymers with conducting and semiconducting properties provide
exciting, promising opportunities for application in electronic devices. Semiconducting polymers
offer the promise of achieving a new generation of materials, exhibiting the electrical and optical
properties of metals or semiconductors and retaining the attractive mechanical properties and
processing advantages of polymers. Many of the envisioned applications of conjugated polymers
require transport of charges and therefore high charge carrier mobility. Hole mobilities in highly
ordered regioregular polythiophenes9 and electron mobilities in ladder type polymers10 as high as 0.1
2
